The Mysterious Inspiral of WASP-12b: Why Obliquity Tides Cannot Drive Orbital Decay
Abstract
WASP-12b's orbit is decaying, for unknown reasons. The planet's period is shrinking more rapidly than can be attributed to equilibrium tides or dynamical tides in a main-sequence star. Planetary obliquity tides could be sufficiently dissipative to drive WASP-12b's inspiral, but would also damp the planet's obliquity, halting the decay. Millholland & Laughlin proposed that a nearby, low-mass planet (∼ 10 M⊕) is maintaining a large obliquity for WASP-12b, sustaining the dissipation. We re-evaluated this hypothesis, finding that the companion must be more massive than originally proposed (≳ 65 M⊕) to absorb WASP-12b's orbital angular momentum. Radial velocity data allowed us to rule out a companion of this type. Any companions within $3$ AU have K ≲ 14 m/s at $95$% confidence.
Related
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BibTeX
@misc{lammers2026mysterious,
title = {{The Mysterious Inspiral of WASP-12b: Why Obliquity Tides Cannot Drive Orbital Decay}},
author = {Caleb Lammers and Yubo Su and Joshua N. Winn},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.11925},
eprint = {2609.11925},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.11925},
}
RIS
TY - UNPB
TI - The Mysterious Inspiral of WASP-12b: Why Obliquity Tides Cannot Drive Orbital Decay
AU - Caleb Lammers
AU - Yubo Su
AU - Joshua N. Winn
PY - 2026
DA - 2026/09/10
PB - arXiv
DO - 10.48550/arxiv.2609.11925
UR - https://arxiv.org/abs/2609.11925
AB - WASP-12b's orbit is decaying, for unknown reasons. The planet's period is shrinking more rapidly than can be attributed to equilibrium tides or dynamical tides in a main-sequence star. Planetary obliquity tides could be sufficiently dissipative to drive WASP-12b's inspiral, but would also damp the planet's obliquity, halting the decay. Millholland & Laughlin proposed that a nearby, low-mass planet (∼ 10 M_⊕) is maintaining a large obliquity for WASP-12b, sustaining the dissipation. We re-evaluated this hypothesis, finding that the companion must be more massive than originally proposed (≳ 65 M_⊕) to absorb WASP-12b's orbital angular momentum. Radial velocity data allowed us to rule out a companion of this type. Any companions within $3$ AU have K ≲ 14 m/s at $95$% confidence.
ER -